If you want to study the difference between Bollywood and serious Indian film-makers, endure Vipul Shah's Namastey London, which opened here last week, and then enjoy Mira Nair's The Namesake, which opens this week. Both are about social and cultural change in the Indian diaspora, and the arranged marriages of lively, intelligent daughters. But Namastey London is an overblown, escapist fantasy featuring caricatures and stereotypes, regularly breaking into song and dance and far removed from everyday life.

The Namesake, adapted by Sooni Taraporevala from a book by the Pulitzer Prize-winning novelist Jhumpa Lahiri, is about the hopes, disappointments, pains and consolations of life over some 40 years as experienced by Ashima (beautiful Bollywood star Tabu), a Bengali girl who marries an Indian scientist Ashoke, (Irfan Khan), settles in America and has two children. The film is dedicated to two towering figures from India's alternative cinema, Bengali directors Ritwik Ghatak and Satyajit Ray, to whom Nair, who has made such films as Salaam Bombay and Monsoon Wedding , is a worthy heir.

The movie begins in 1974 with Ashoke reading Gogol's collected stories on a train while being lectured on the need to travel the world by a middle-aged fellow passenger. There's a sudden crash which Ashoke miraculously survives. Three years later, while a graduate student of fibre optics in New York, he returns to India to marry Ashima. She never quite settles in the States, spending much of her time among fellow exiles from the subcontinent, though she does make friends with a fellow librarian when the family move upmarket and up the Hudson to fashionable Nyack.

They have two children, a boy, Gogol (Kal Penn), and a daughter, Sonia (Sahira Nair), who grow up to be bright, middle-class Americans. Gogol studies architecture at Yale and plans to marry the daughter of rich Wasps. Sonia settles in California with a white American boy.

Though full of incident and sharp observation and extremely well-acted, this elliptical movie constantly jumps several years in a single cut and the characters are on the thin side. The overall feeling is of a six-hour mini-series cut down to 122 minutes for theatrical release.

Still, it is a considerable achievement, assured, moving, often very funny. Its title refers to Gogol the writer and Ashima's son, and, at first, we think it is some sort of whim connected with Ashoke's amazing survival. His son reacts against the name and, as a student, exchanges it for Nick, which derives from his other name. But it transpires that Ashoke thinks the Russian author's career and work reflect his own life of exile and disappointment, and he remarks that 'we all come out of Gogol's "Overcoat"', an observation variously attributed to Dostoevsky, Tolstoy and Turgenev. Anyway, the film sent me back to 'The Overcoat'.